1. Technical Field
This disclosure relates to devices used for charging portable devices.
2. Description of the Related Art
A large variety of portable devices has recently appeared on the market, such as laptop computers, notepads, mobile telephones, personal digital assistants, music and video players, cameras and video cameras. The common features of these devices are that they can all be battery-operated and have compatible connection interfaces allowing them to be connected to a computer, laptop or other, especially for exchanging data. The most commonly used connection interfaces are USB (Universal Serial Bus) and IEEE 1394 (“Firewire”).
A proposal has therefore been made to charge the batteries of these small portable devices through these connection interfaces with the device connected to a computer. This charging method is possible even with a laptop computer not connected to a charger, in other words, operating on its battery, since the latter is significantly larger than that of a device like a mobile telephone.
In some laptop computer configurations, the connection interface feeds power supply and/or charging voltage to a connected device, regardless of the power status of the laptop computer, and especially even if it is not switched on. In other laptop computer configurations, especially in the case of notepads or so-called “ultraportable” computers, the connection interface is set to a low power mode in which it only supplies low power supply voltage without enabling any charging of a device, or only charging of devices powered by very small batteries. In both of these configurations, an interface control circuit may or may not have detected the presence of a connected device. The connected device decides autonomously to stop the charging process, but does not usually provide the charger with any information concerning this status change. Only devices operating an energy management protocol can supply this information, and this information is only used if the computer supplying the charging voltage is not in standby mode.